Organic Light Emitting Diode (OLED) display screens have become the display technology of the next generation having promising future due to their advantages, such as thinness, lightness, wide visual angle, active light-emitting, continuously tunable luminous colors, low costs, fast response, low energy consumption, low driving voltages, wide range of operation temperatures, simple fabricating process, high luminous efficiency, flexible display etc.
The basic structure of an OLED comprises an anode and a cathode with an organic light emitting layer disposed therebetween. The organic light emitting layer is driven by an applied electric field and gives rise to a luminescence phenomenon through injection and recombination of carriers from the anode and the cathode respectively. Specifically, electrons and holes, as carriers, are injected from the cathode and anode respectively, migrate to the organic light emitting layer under the action of the electric field, and recombine there resulting in excitors, which release energy with their attenuation, the released energy exciting the luminous molecules to emit visible light through radiative relaxation of the excited luminous molecules.
OLEDs are classified into passive matrix OLEDs (PMOLEDs) and active matrix OLEDs (AMOLEDs) according to the driving modes. With respect to a PMOLED, cathodes and anodes are arranged in a matrix, and pixels in an array are lit in a sweeping manner with each pixel operating in a short pulse mode. A PMOLED has a simple structure to illuminate instantaneously with a high brightness, which can reduce manufacturing costs effectively, but PMOLED requires a relatively higher driving voltage and thus is not applicable to a large-sized display panel with a high resolution. With respect to an AMOLED, each pixel is controlled by an individual thin film transistor (TFT) and driven to illuminate individually and continuously. An AMOLED requires a relatively low driving voltage, has a relatively long service life, and thus is applicable to a large-sized flat panel display, however its fabricating process is relatively complex and its costs are relatively high.